ELi5 why does toilet water never rise above “set” level? You flush toilet? Water level inside of it doesn’t rise over the “set level” and etc.

Question

ELi5 why does toilet water never rise above “set” level? You flush toilet? Water level inside of it doesn’t rise over the “set level” and etc.

In: Engineering

Answer 1

The bowl isn’t a closed system. It has a drain in the back. That drain pipe uses a bend to trap water to prevent gas coming from the sewer/septic system into your house. As you fill the bowl with water, the water level rises in the trap until it reaches the top of that bend and flows out the drain. That is why the toilet never rises above that certain level. That height is the level of the drain. The toilet bowl only overflows when that drain becomes blocked.

This wiki article gives some images for the trap:

[https://en.wikipedia.org/wiki/Trap_(plumbing)](https://en.wikipedia.org/wiki/Trap_(plumbing))